Sri vidya college of engineering and technology

PREFABRICATED STRUCTURES

www.Vidyarthiplus.com

www.vidyarthiplus.com

CE6016 PREFABRICATED STRUCTURES L T P C

3 0 0 3

OBJECTIVES:

To impart knowledge to students on modular construction, industrialised construction and design of

prefabricated elements and construction methods.

UNIT I INTRODUCTION 9

Need for prefabrication – Principles – Materials – Modular coordination – Standarization –Systems –

Production – Transportation – Erection.

UNIT II PREFABRICATED COMPONENTS 9

Behaviour of structural components – Large panel constructions – Construction of roof and floor slabs – Wall panels

– Columns – Shear walls

UNIT III DESIGN PRINCIPLES 9

Disuniting of structures- Design of cross section based on efficiency of material used – Problems in design because of

joint flexibility – Allowance for joint deformation.

UNIT IV JOINT IN STRUCTURAL MEMBERS 9

Joints for different structural connections – Dimensions and detailing – Design of expansion joints

UNIT V DESIGN FOR ABNORMAL LOADS 9

Progressive collapse – Code provisions – Equivalent design loads for considering abnormal effects such as

earthquakes, cyclones, etc., - Importance of avoidance of progressive collapse.

TOTAL: 45 PERIODS

OUTCOMES:

The student shall be able to design some of the prefabricated elements and also have the knowledge of the

construction methods in using these elements.

TEXTBOOKS:

1. CBRI, Building materials and components, India, 1990

2. Gerostiza C.Z., Hendrikson C. and Rehat D.R., "Knowledge based process planning for construction and

manufacturing", Academic Press Inc., 1994

REFERENCES:

1. Koncz T., "Manual of precast concrete construction", Vol. I, II and III, Bauverlag, GMBH,

1976.

2. "Structural design manual", Precast concrete connection details, Society for the studies in the use of precast

concrete, Netherland Betor Verlag, 2009



UNIT I

INTRODUCTION

PREFABRICATION

Prefabrication is the practice of assembling components of a structure in a factory or other

manufacturing site and transporting complete assembles to the construction site where the structure is

to be located. Prefabricated building is the completely assembled and erected building of which the

structural parts consist of prefabricated individual units or assemblies using ordinary or controlled

materials. Prefabricated construction is a new technique and is desirable for large scale housing

programmes.

Prefabricated building:

Prefabricated building is a type of building that consists of several factory-built

components or units that are assembled on-site to complete the unit.

The term 'prefabricated' is buildings built in components (e.g. panels), modules (modular

homes), transportable sections (manufactured homes),It may also be used to refer to

mobile homes.

Different Between Prefabricated Constructions and Conventional Type:

The conventional method of building a house is to transport bricks, timber,

cement, sand, and construction aggregate, etc to the site, and to construct the house on

site from these materials. In prefabricated construction, only the foundations and floor

slabs are constructed in this way, while sections of walls and roof are prefabricated

(assembled) in a factory (possibly with window and door frames included), transported to

the site, lifted into place by a crane and bolted together



PRINCIPLES: (AIMS)

1) To effect economy in cost

2) To improve in quality as the components can be manufactured under controlled conditions.

3) To speed up construction since no curing is necessary.

4) To use locally available materials with required characteristics.

5) To use the materials which possess their innate characteristics like light weight, easy

workability, thermal insulation and combustibility etc.

NEED FOR PREFABRICATION

Cost of construction

shorter construction time

easy of expansion

utilization of material

attractive finishes

highly efficient for weather resistance

single source assurance

insurance advantage

Prefabricated structures are used for sites which are not suitable for normal construction method

such as hilly region and also when normal construction materials are not easily available.

PFS facilities can also be created at near a site as is done to make concrete blocks used in plane of

conventional knick.

Structures which are used repeatedly and can be standardized such as mass housing storage sheds,

godowns, shelter, bus stand security cabins, site offices, fool over bridges road bridges. Tubular

structures, concrete building blocks etc., are prefabricated structures

Material Properties In of Prefabricated Structures

Quick to assemble



Cost-effective

Portable/movable

Strong

Waterproof, Moisture proof

Fire Resistant

Prefabrication Types:

1. Conventional prefabrication construction is the most traditional construction

method where all the construction activities are in-situ practices on site:

2. Semi-prefabrication divides as two sub-categories: system formwork and non-

structural semi-prefabrication, involving a part of in-situ construction activities

and a part of prefabrication. Normally, the non-structural semi-prefabrication is

applied on façade, curtain walls, lost form systems and dry wall systems;

3. Comprehensive prefabrication involves a structural part and pre-finished

construction. Examples of applications of structural comprehensive prefabrication

include staircases, slabs, columns and beams: and

4. Volumetric off-site fabrication encloses usable space but does not constitute the

whole building. Volumetric off-site fabrication is mainly used for ‘facilities’ and

includes solutions on office washrooms, plant rooms, building services risers and

lifts.

PROCESS OF PREFABRICATION

An example from house building illustrates the process of prefabrication. The conventional

method of building a house is to transport bricks, timber, cement, sand, steel and construction

aggregate etc. to the site and to construct the house on site from these materials.

In prefabricated construction only the foundations are constructed in this way. While sections of walls

floors and roof are prefabricated structures with windows and door frame included and transported to

the site lifted in to place by a crane and boiled together.

USES OF PREFABRICATION



1. The most widely used form of prefabrication building and civil engineering is the use

of prefabrication concrete & prefabricated steel sections in structures where a

particular part or form is repeated many times.

2. Pouring concrete sections in a factory brings the advantages of being able to re-use

moulds and the concrete can be mixed on the spot without having to be transported to

and pumped wet on a congested construction site.

3. Prefabricating steel sections reduces on-site cutting and welding costs as well as the

associated hazards.

4. Prefabrication techniques are used in the construction of apartment blocks and housing

developments with repeated housing units.

5. The technique is also used in office blocks, warehouses and factory buildings.

6. Prefabricated steel and glass section are widely used for the exterior of large buildings.

7. Prefabricated bridge elements and systems offer bridge designers & contractors

significant advantages in terms of construction time safety environmental impact

constructability and cost.

8. Prefabrication can also help minimize the impact on transfer from bridge building.

9. Radio towers for mobile phone and other services often consist of multiple

prefabricated sections.

10. Prefabricated has become widely used in the assembly of aircraft and space craft with

component such as wings and fuselage sections often being manufactured in different

countries or states from the final assembly site.

ADVANTAGE OF PREFABRICATION

Self supporting readymade components are used so the need for formwork shuttering and

scaffolding is greatly reduced.

Construction time is reduced and buildings are completed sooner allowing on earlier return of

the capital invested.

On-site construction and congestion is minimized.



Quality control can be easier in a factory assembly line setting than a construction site setting.

Prefabrication can be located where skilled labour, power materials space and overheads are

lower.

Time spent in bad weather or hazardous environments at the construction site is minimized

Materials for scaffolding is stored partly or in full and used

Availability of precise structure and expect workmanship.

Less waste may be generated and in a factory setting it may be easier to recycle it

back into the manufacturing process, for instance it is less costly to recycle scrap

metal generated in a metal fabrication shop than on the construction site.

On-site construction and congestion is minimized.

Work time is reduced.

Fewer expansion joints are required.

Interruptions in connecting can be omitted.

Work is done with a better technology.

Less workers are needed.

Members can be used again.

DISADVANTAGES OF PREFABRICATION

Careful handling of prefabricated components such as concrete panels or steel and glass panels

is required.

Attention has to be paid to the strength and corrosion-resistance of the joining of prefabricated

sections to avoid failure of the joint

Similarly leaks can form at joints in prefabricated components.

Transportation costs may be higher for voluminous prefabricated sections than for the

materials of which they are made which can often be packed more efficiently.

Large prefabricated structures require heavy-duty cranes & precision measurement and

handling to place in position.

Large groups of buildings from the same type of prefabricated elements tend to look drab and

monotonous.

Local Jobs are lost.



The main reasons to choose precast construction method over conventional in situ method

1. Economy in large scale project with high degree of repetition in work execution.

2. Special architectural requirement in finishing

3. Consistency in structural quality control

4. Fast speed of construction

5. Constraints in availability of site resources (e.g. materials & labour etc.)

6. Other space & environmental constraints

7. Overall assessment of some or all of the above factors which points to the superiority of

adopting precast construction over conventional method.

The following details gives the cost implications of precast construction & conventional in-

situ method.

MATERIALS USED:

Prefabricated building materials are used for buildings that are manufactured off site and

shipped later to assemble at the final location some of the commonly used prefabricated building. The

materials used in the prefabricated components are many. The modern trend is to use concrete steel,

treated wood, aluminium cellular concrete, light weight concrete, ceramic products etc. While

choosing the materials for prefabrication the following special characteristics are to be considered.

Light weight for easy handling and transport and to economic an sections and sizes of

foundations

Thermal insulation property

Easy workability

Durability in all weather conditions

Non combustibility

Economy in cost

Sound insulation

CHARACTERISTICS OF MATERIALS

Easy availability



Light weight for easy handling and transport and to economies on sections and seizes of

foundations.

Thermal insulation property

Easy workability

Durability to all weather conditions

Non combustibility

Economy in cost

MATERIALS ARE ALUMINUM, STEEL, WOOD, FIBERGLASS AND CONCRETE

Prefabricated metal buildings use galvanized steel and galvalume as the chief materials for

building. Galvalume is a form of steel coated with aluminium zinc. This is to protect the building

against corruption rust and fire. It also provides a study and protective covering to the prefabricated

building. Almost all the components of a metal building such as beams, frames columns wall & roofs

are made of steel. Most fabricated military buildings use steel or aluminium frames.

[Synthetic materials are used for the walls & roofs. To provide enhanced security a combination of

both metal and cloth materials are used plastic flooring materials can be quickly assembled and are

very durable]

Prefabricated building materials used for small prefabricated buildings are steel, wood, fibre glass

plastic or aluminium materials. These materials are cheaper than regular brick and concrete buildings.

Materials like steel, fibre glass, wood and aluminium are used as prefabricated building materials for

sports buildings. These materials provide flexibility and are preferred for making structures and

accessories like stands and seats for stadium and gyms.

For making low cost houses prefabricated materials like straw bale, Ferro cement consists of a cement

matrix reinforced with a mesh of closely spaced iron rods or wires. In this type of construction the

techniques used are simple & quick.

Using prefabricated material one can make durable, water and fire resistant and cheap prefabricated

buildings Most of the prefabricated building materials are eco-friendly & affordable.

MODULAR COORDINATION



. Modular coordination or MC is a dimensional system. It is a dimension and space

coordination concept in which building and components are placed at their designations

based on the unit or basic module known as "1M" that equals to 100 mm. The use of MC

is an important factor in IBS effective application as it completes the industry through

quality control and increase of productivity.

The modular coordination is defined as the basic module is in adopted the size of which is

selected for general application to building and its components. The value of the basic module chosen

is 100 mm for maximum flexibility and convenience. The symbol used for basic module is M

1M = 100mm

100mm = 1M = It is international standard value.

Dimensional coordination employing the basic module or a multimodule. The purposes of modular

coordination are

i. To reduce the variety of component size produced

ii. To allow the building designer greater.

AIMS OF MODULAR COORDINATION

Major Objective

Specific Objective

MAJOR OBJECTIVE

The principal object of modular coordinate is to assist the building design construction professional

building industry and its associated manufacturing industries by standardization in such a way that

building components fit with each other with other components and with building assembly on site

thereby improving the economics of building.

SPECIFIC OBJECTIVES

Modular coordination thus



- Facilities cooperation between building designers manufacturers distributors contractors and

authorities.

- In the design work enables buildings to be so dimensionally coordinated that they can be

erected with standard components without undue restriction on freedom of design.

- Permits a flexible type of standardization. This encourages the use of a number of

standardized building components for the construction of different types of buildings.

- Optimize the number of standard sizes of multimodal’s will suit particular applications.

However if modular coordination is to be achieved the values of multimodal’s should not be

chosen arbitrarily and only standardized multimodal’s shall be used pay using multimodal’s it is

possible to achieve a substantial reduction in the number of modular sizes particularly for components

having at least one dimension equal to one of the dimensions of the functional element of which they

are a part.

A further reduction in the number of modular sizes for components having may be achieved by

mean of as general series of multi modular sizes based on selected multimodal’s for horizontal

coordinating dimensions are 3M , 6M, 12M, 30M & 60M

The multimode 15M may also be used for special applications

MODULES

Modules are a standard unit of size used to coordinate the dimensions of buildings and components.

Modules

Bsic Multimodules



MULTI MODULES

Multi modules are standardized selected whole multiples of the basic module different single T beam

has resulted the beam to fall 2 basement down. The beam just placed for connection.

BASIC MODULE

The fundamental module used in modular coordination the size of which is selected for general

application to buildings and components

MODULAR CO-ORDINATION DIMENSION:

1) The planning grid in both directions of the horizontal plan shall be:

a. 3m for residential and institutional buildings

b. For industrial buildings,

15M for spans up to 12m

30M for spans between 12m and 18m and

60M for spans over 18m

The centre lines of load bearing walls shall coincide with the grid lines.

2) Incase of external walls, the grid lines shall coincide with the centre line of the wall 50mm from

the internal force.

3) The planning module in the vertical direction shall be 1M up to end including a height of 2.8m,

above the height of 2.8m it shall be 2M.

4) Preferred increments for sill heights, doors, windows etc. shall be 1M.

5) In case of internal columns, the grid lines coincide with the centre lines of columns. In case of

external columns and columns near the lift and stair wells the grid lines shall coincide with centre

lines of the column in the top most storey or a line in the column 50mm from the internal face of

column in the top most storey.

Modular Grid



A rectangular coordinate reference system in which the distance between consecutive lines is the

basic module or a multimodule. This multimodule may differ for each of the two dimensions of the

grid.

Type of Modular Grid

There are different types of grid patterns which are used to locate the positions and dimensions of

building spaces components are

Elements in building design

Continuous grid

Superimposed grid

Displacement of grid (or) Tartan grids

Interrupted grids as neutral zones.

Continuous grid

Where all dimensions in either direction are based on one increment only.

Superimposed grids

When the modulur grid of 100 mm increment is superimposed on a multi-modulur grid.

Displacement of grid or tartan grids

Where there is a homogenous and repetitive relation between at least two basic increments.

Eg:- 1M +2M (or) 3/2 M + 3M

Interrupted grids (or) neutral zones

Where there are non modular interruptions of grids neutral zones are created to cope with the

economics of building design.



Benefits Of Modular Coordination

Modular Coordination is a useful design tool that provides modern designprinciples and rules which combine freedom in architectural planningand free choice of construction method, with the possibility ofincorporating standardised modular components in the project. Whenapplied throughout the industry, it brings the following benefits:

(a) better coordination and cooperation between various parties in construction;

(b) reduction in design time, especially with the use of standard detailsand dimensional coordination;

(c) benefits through the increased use of Computer Aided Design and Drafting;

(d) reduction in manufacturing and installation costs;

(e) reduction in the wastage of materials, time and manpower in cuttingand trimming on site;

(f) facilitating prefabrication.

As in the case of introducing a new machinery, designers who intend toapply the Modular Coordination principles must realise that it would requireconsiderable effort and discipline and the process may not be pleasant,at least initially. However, in the long term, it is likely to payoff whenthe tool is understood and used effectively; more so if implementedthroughout the industry.



MODULAR HOMES

Modular homes are houses divided into multiple modules / sections which are

manufactured in a remote facility and then delivered to their intended site of use. The

modules are assembled into a single residential building using either a crane or trucks.

Steel and/or wood framing are common options for building a modular homes. Modular

components are typically constructed within a large indoor facility on assembly lines.

uch dwellings are often priced lower than their site-built counterparts and are typically

more cost-effective to builders and consumers. These new homes can be constructed in

less time than it takes to build a home "on-site“.

Importance of modular homes

1. Indoor construction. Assembly is independent of weather which increases work

efficiency and avoids damaged building material.



2. Favourable pricing from suppliers. Large-scale manufacturers can effectively

bargain with suppliers for discounts on materials.

3. Ability to service remote locations. Particularly in countries such as Australia

there can be much higher costs to build a site-built house in a remote area or an

area experiencing a construction boom such as mining towns. Modular homes can

be built in major towns and sold to regional areas.

4. Low waste. With the same plans being constantly built, the manufacturer has

records of exactly what quantity of materials is needed for a given job. While

waste from a site-built dwelling may typically fill several large dumpsters, waste

from a modular dwelling generates much less waste.

5. Building Strength. According to manufacturers, modular homes are generally

designed to be initially stronger than traditional homes.For example, replacing

nails with screws and adding glue to joints. This is supposed to help the modules

maintain their structural integrity as they are transported on trucks to the

construction site.

6. Assembly Time. The modules that will combine to form the house are assembled

off-site in a factory. These modules can take one to three months to be constructed

but often take as little as 10 days to actually construct when they are first started.

Then they are transported to the building site where a crane is brought in to

assemble the modules together.The placement of the modules together generally

takes several hours or days.



Modular homes

Indoor Construction of modular homes

S

Mobile Homes

Mobile homes or static caravans are prefabricated homes built in factories, rather than on

site, and then taken to the place where they will be occupied. They are usually

transported by tractor-trailers over public roads to sites which are often in rural areas or

high-density developments. In some countries they are used for temporary



accommodation on campsites. While these houses are usually placed in one location and

left there permanently or they have the ability to be move.

Behind the work fitted at installation to hide the base, there are strong trailer frames,

axles, wheels and tow-hitches. The two major sizes are single-wides and double-wides.

1. Single-wides are eighteen feet or less in width and 90 feet (27 m) or less in length

and can be towed to their site as a single unit.

Double-wides are twenty feet or more wide and are 90 feet (27 m) in length or less and

are towed to their site in two separate units, which are then joined together.



Mobile homes

STANDARDIZATION

Standardization is to the creation and use of guidelines for the production of uniform

interchangeable components especially for use in mass production. It also refers to the establishment

and adoption of guidelines for conduct to global marketing the term is used in describe the

simplification of procurement & production to achieve economy

ADVANTAGES OF STANDARDIZATION

1) Easier in design as it eliminates unnecessary choices

2) Easier in manufacture as there are limited number of variants.

3) Makes repeated use of specialized equipments in erection and completion

4) Easier and quicker.

FACTORS INFLUENCING STANDARDIZATION:-

1) To select the most rational type of member for each element from the point of production,

assembly, serviceability and economy.

2) To limit the number of types of elements and to use them in large quantities.



3) To use the largest size of the extent possible, thus resulting in less number of joints.

4) To limit the size and number of prefabricate by the weight in overall dimension that can be

handled by the handling and erection equipment and by the limitation of transportation.

5) To have all these prefabricates approximately of same weight very near to the lifting capacity

of the equipment.

SYSTEMS

The word system is referred to a particular method of construction of buildings by using

prefabricated components which are inter-related in functions and are produced to a set of instructions

with certain constraints. Several plans are possible using the same set of components. The degree of

flexibility varies from system to system.

CHARACTERISTICS OF A PREFABRICATION SYSTEM:-

The following characteristics among others are to be consideration devising a system.

1) Intensified usage of spaces.

2) Straight and simple walling scheme.

3) Limited sizes and number of components.

4) Limited opening in bearing walls.

5) Regulated locations of partitions.

6) Standardized service and stair units.

7) Limited sizes of doors and windows with regulated positions.

8) Structural clarity and efficiency.

9) Suitability for adoption in low rise and high rise blocks.

10) Ease of manufacturing, storing and transporting.

11) Speed and ease of erection.

12) Simple jointing system.

PREFABRICATED CONSTRUCTION SYSTEMS:-

The system of prefabricated construction depends on the extent of the use of prefabricated

components, their material, sizes and the technique adopted for their manufacture and use in building.

The various prefabrication systems are outlined below.



1) Small prefabrication

2) Medium prefabrication

3) Large prefabrication

4) Open prefabrication system

a. Partial prefabrication open system

b. Full prefabrication open system

5) Large panel prefabrication system

6) Wall system

a. Cross wall system

b. Longitudinal wall system

7) Floor system

8) Stair case system

9) Box type system

SMALL PREFABRICATION

The first 3 types are mainly classified according to their degree of precast elements using in that

construction. for eg:- brick is a small unit precasted and used in buildings. This is called as small

prefabrication. That the degree of precast element is very low

MEDIUM PREFABRICATION

Suppose the roofing systems and horizontal member are provided with precast elements. These

constructions are known as medium prefabricated construction. Here the degree of precast elements

are moderate.

LARGE PREFABRICATION

In large prefabrication most of the members like wall panels, roofing/flooring systems, beams and

columns are prefabricated. Here degree of precast elements are high.

OFF-SITE (FACTORY) PREFABRICATION



One of the main factors which affect the factory prefabrication is transport. The width of road walls

mode of transport vehicles are the factors which factor the prefabrications which is to be done on site

or factory.

Suppose the factory situated at a long distance from the construction site and the vehicle have to cross

a congested traffic with heavy weighed elements the cost in-situ prefabrication is preferred even

though the same condition are the cast in site prefabrication is preferred only when number of houses

are more for small elements the conveyance is easier with normal type of lorry and trailors. Therefore

we can adopt factory (or) OFF site prefabrication for this type of construction.

OPEN PREFABRICATION SYSTEM:-

This system is based on the use of the basic structural elements to form whole or part of a building.

The standard prefabricated concrete components which can be used are,

1) Reinforced concrete channel units

2) Hollow core slabs

3) Hollow blocks and battens

4) Precast plank and battens

5) Precast joists and tiles

6) Cellular concrete slabs

7) Prestressed / reinforced concrete slabs

8) Reinforced / prestressed concrete slabs

9) Reinforced / prestressed concrete columns

10 Precast lintels and sunshades

11 Reinforced concrete waffle slabs / shells

12 Room size reinforced / prestressed concrete panels

13 Reinforced / prestressed concrete walling elements

14 Reinforced / prestressed concrete trusses

The elements may be cost at the site or off the site.

Foundation for the columns could be of prefabricated type of the conventional cast in situ type

depending upon the soil conditions and loads. The columns may have hinged or fixed base

connections depending upon the type of components used and the method of design adopted.



There are two categories of open prefabricated systems depending on the extent of

prefabrication used in the construction as given below.

1) Partial prefabrication open system

2) Full prefabrication open system

PARTIAL PREFABRICATION OPEN SYSTEM:

The system basically emphasizes the use of precast roofing and flooring components and other

minor elements like lintels, sunshades, kitchen sills in conventional building construction. The

structural system could be in the form of insitu frame work or load bearing walls.

FULL PREFABRICATION OPEN SYSTEM:

In this system, almost all the structural components are prefabricated. The filler walls may be

of bricks or of any other local materials.

LARGE PANEL PREFABRICATION SYSTEM:

This is based on the use of large prefabricated components. The components used are precast

concrete large panels for walls, floor roofs, balconies, stair cases etc. The casting of the components

could be at the site or off the site.

Depending upon the context of prefabrication, this system can also lend itself to partial

prefabrication system and full prefabrication system.

WALL SYSTEM:

Structural scheme with precast large panel walls can be classified as

1) Cross wall system

2) Longitudinal wall system



CROSS WALL SYSTEM:

In this system the cross walls are load bearing walls. The facade walls are non-load bearing. This

system is suitable for high rise buildings.

LONGITUDINAL WALL SYSTEM:

In this system, cross walls are non-bearing, longitudinal walls are load bearing. This system is suitable

for low rise buildings.

A combination of the above systems with all load bearing walls can also be adopted.

Precast concrete walls could be



1) Homogeneous walls

2) Non-homogeneous walls

Homogeneous walls:

The walls could be solid or ribbed.

Non-homogeneous walls:

Based on the structural functions of the walls, the walls could be classified as

a. Load bearing walls

b. Non-load bearing walls

c. Shear walls

Based on their locations and functional requirements the walls are further classified as

(i) External walls which can be load or non-load bearing depending upon the layout. They

are usually non-homogeneous walls of sandwiched type to impart better thermal

comforts.

(ii) Internal walls which provide resistance against vertical loads, horizontal loads, fire etc.

and are normally homogeneous.



TYPES OF PRECAST FLOORS:

Depending upon the composition of units, precast flooring units could be homogeneous or

non-homogeneous.

1) Homogeneous floors could be solid slabs, cored slabs, ribbed or waffle slabs.

2) Non-homogeneous floors could be multilayered ones with combinations light weight

concrete or reinforced / pre stressed concrete with filled blocks.

Depending upon the way, the loads are transferred the precast floors could be classified as one

way or two way systems.

ONE WAY SYSTEM:-

One way system transfers loads to the supporting members in one direction only. The precast

elements of this category are channel slabs, hollow core slabs, hollow blocks and hollow plank

system, channels and tiles system, light weight cellular concrete slab etc.

TWO WAY SYSTEMS:-

Transfer loads in both the direction imparting loads on the four edges. The precast element

under this category are room sized panels two way ribbed or waffle slab system etc..

STAIR CASE SYSTEM:-

Stair case system consists of single flights with inbuilt risers and treads in the element only.

The flights are normally unidirectional transferring the loads to supporting landing slabs or load

bearing walls.

BOX TYPE SYSTEM:-

In this system, room size unit are prefabricated and erected at site. This system derives its

stability and stuffiness from the box limits which are formed by four adjacent walls. Walls are joined

to make rigid connections among themselves. The box unit rest as plinth foundation which may be of

conventional type of pre-cast type.

SYSTEMS PRODUCTION



The term production of systems is describes a series of operation directly concerned In the

process of making or more apply of moulding precast units on the face of it there are very many

techniques since almost every type prefabricates requires a specific series of operation in its

production.

These techniques however may be grouped into three basic method of production. These are

1. The stand system

2. The conveyor belt or production line system

3. The aggregate system

Stand system

In the stand system the prefabricates mature at the point where they were moulded

While the production team moves to successive stands the bed on which prefabricates.

Conveyor belt

The conveyor belt system of production splits the whole production process in to a series of

operation carried out at a separate successive and permanent point to the heat may be by means of

conveyor belt trolleys & crane etc.

Aggregate system

The word aggregates describes a large, complex permanently installed set of machines and

mechanical application which can carry out most of the separate operation involved in casting

concrete components.

PRODUCTION

Considerations in production

The general rule is that the connection device must be as ‘foolproof’ as possible. It

should be possible to place it in the mould correctly oriented and within the necessary

tolerances, with a minimum of effort.

1. Avoid congestion



At the location of connections additional reinforcing steel, embedded plates,

inserts, block-outs etc. are frequently required. It is not unusual that so many items are

concentrated in a small location that very little room is left for the concrete. It must be

kept in mind that reinforcing bars and prestressing strands, which appear as lines on the

drawing, take up real space in the elements. Reinforcing bars require more space than

their nominal diameter, and there must be room for the curvature of bent bars. If

congestion is suspected, it is helpful to draw large-scale details of the region in question.

2. Avoid penetration of the forms

Units requiring holes in the forms should be avoided if possible, especially in steel

moulds. Exceptions to this rule can be made if there is a substantial amount of repetition

in the production. Holes in the forms may be necessary not only because the units are



protruding from the elements, but also for the arrangement used to keep the units in place

during casting. The units must also be designed so that they do not make the dismantling of

the form impossible without damage to the form. Most forms are supposed to be used more

than once. Connection units to be placed in the top surface during casting should be secured

against the edges of the mould using purpose made holding devices. These devices are

mostly costly, make it more difficult to obtain a smooth surface, or the holding

device may hamper the placement of concrete or other surface material. The various

disadvantages have to be evaluated before selecting the method. However, if the same steel

plate is placed in the bottom of the form, it can be located with great accuracy, as it can be

fixed to the bottom directly.

3. Reduce post-stripping work

A plant casting operation is most efficient when the product can be taken directly

to the storage area immediately after removal from the form. Any operations required

after stripping and before erection, such as special cleaning or finishing, welding on

projecting hardware etc. should be avoided. These operations require additional handling

(increased possibility of damage to the elements), extra workspace and added labour,

often with skilled trades. Sometimes a trade-off is necessary between penetration of the

forms and post-stripping work.

4. Use repetitious details

It is very desirable to repeat details as much as possible. Similar details should be

identical, even ifit results in a slight over-design.

5. Use standard items

Hardware items such as inserts, studs, steel elements, etc., should be readily

available standard items that are preferably from more than one supplier. It also

simplifies fabrication if similar product items are standardised as to size and shape. There

is also less chance of error. The same principle applies to reinforcing bars, embedded

plates, etc.



6. Be aware of material limitations

Examples of this are the radius requirements for bending reinforcing bars, standard

lengths for

certain sizes of inserts, etc.

7. Avoid non-standard tolerances

Dimensional tolerances, which are specified to be more rigid than industry

standards, are difficult to achieve. Connections, which require close-fitting parts without

provision for adjustment, should be avoided as much as possible.

8. Allow alternatives

Very often precasters will prefer certain details. The producer should be allowed

to use alternative methods or materials, provided the design requirements are met.

Allowing alternative solutions willoften result in the most economical and best

performing connections.

The location of precasting yards consist of storage facilities suitable for transporting and

erection equipments and availability of raw materials are the critical factors which should be carefully

planned and provided for effective and economic use of pre-cast concrete components in construction.

The manufacture of the components can be done in a centrally located factor of in a site where

precasting yards set-up at or near the site of work.

FACTORY PREFABRICATION;

Factory prefabrication is restored in a centrally located plant for manufacture of standardized

components on a long form basis.

It is a capital intensive production where work is done throughout the year preferably under a covered

shed to avoid the effects of seasonal variations high level of mechanization can always be introduced

in this system where the work can be organized in a factory like manner with the help of constant

team of workmen.



The basic disadvantage in factory prefabricated, is the extra cost in occurred in transportation of

elements from plant to site of work sometimes the shape and size of prefabricable are to be limited

due to lack of suitable transportation equipment roads controls etc.

SITE PREFABRICATION:

In this scheme, the components are manufactured at site near the site of work as possible. This

system is normally adopted for a specific job order for a short period. The work is normally carried

out in open space with locally a valuable labour force. The equipment machinery and moulds are of

mobile nature.

Therefore there is a definite economy with respect to cost of transportation. This system

suffers from basic drawback of its non-suitability to any high degree of mechanization. It has no

elaborate arrangements for quality control.

PROCESS OF MANUFACTURE:

The various processes involved in the manufacture of precast elements are classified as

follows:

1) Main process

2) Secondary (auxiliary) process

3) Subsidiary process

MAIN PROCESS:

It involves the following steps.

1) Providing and assembling the moulds, placing reinforcement cage in position for reinforced

concrete work, and

2) Fixing of inserts and tubes where necessary.

3) Depositing the concrete in to the moulds.

4) Vibrating the deposited concrete into the moulds.

5) Demoulding the forms.

6) Curing (steam curing if necessary)

7) Stacking the precast products.



SECONDARY (AUXILLARY) PROCESS:

This process is necessary for the successful completion of the process covered by the main

process.

1) Mixing or manufacture of fresh concrete (done in a mixing station or by a matching plant).

2) Prefabrication of reinforcement cage (done in a steel yard of workshop)

3) Manufacture of inserts and other finishing items to be incorporated in the main precast

products.

4) Finishing the precast products.

5) Testing the precast products.

STAGES OF PREFABRICATED CONCRETE PRODUCT:

Stage

process

1 Procurement storage of row materials

2 Testing of raw materials

3 Design of concrete mix

4 Fabrication of reinforcement cages

5 Oiling and laying of moulds in portion

6 Placing of reinforcement cages inserts

and fixtures

7 Preparation of fresh concrete

8 Transport fresh concrete

9 depouring into moulding etc.

10 Curing of concrete

11 Stacking of pre-cost element

12 Testing of finished component



FLOW DIAGRAM OF STAGES OF PROCESSING

CONCRETE---------MOULD-----------------STEEL

MIXING--------------PREPARATION--------CUTTING

FILLING----------------------------------------REINFORCING

COMPONENT

COMPACTION

CURING

DEMOULDING

STORAGE

STORAGE OF PRE-COST CONCRETE PRODUCTS BY STAGE

PRODUCTION TOLERANCE (T)

The limits of deviation in the dimensions (Δs) T/2 the shape of the prefabricates. This depends

very much on the type of moulds, wooden, steel, concrete or plastic the tolerance also depends on the

nominal dimension, nature of prefabricate and its position during casting.

Degree of

accuracy

≤10 cm › 10 cm

≤ 30 cm

730 cm

≤ 3 m

3 m

≤ 9 m

› 9 m

4

5

6

7

8

1 mm

2 mm

3 mm

4 mm

6mm

2 mm

3

4

6

10

3 mm

4

6

10

15

4 mm

6

10

15

25

6 mm

10

15

25

30



TRANSPORT

Transport of prefabrication elements must be carried out and with extreme care to avoid any

flock and distress in elements and handled as far as possible to be placed in final portion

Transport of prefab elements inside the factory depends on the method of production selected for

the manufacture.

Transport of prefab elements from the factory to the site of action should be planned in

conformity with the trafficable rules and regulations as stipulated by the authouritic the size of the

elements is often restricted by the availability of suitable transport equipment, such as tractor-am-

tailor, to suits the load and dimension of the member in addition to the load carrying capacity of the

bridges on the way.

While transporting the prefab elements in various systems, such as wages, trucks, bullock

cards etc. care should be taken to avoid excessive cantilever actions and desired supports are

maintained. Special care should be taken in negotiating sharp beds uneven of slushy roads to avoid

undesirable stresses in elements and in transport vehicles. Before loading the elements in the

transporting media, care should be taken to ensure the base packing for supporting the elements are

located at specified portion only.

Considerations for transportation

During transportation any units protruding from the concrete element must be shielded in

order not to create a hazard to people. Protruding units must be able to withstand any

shocks they can be subjected to during handling. Protruding units, like reinforcing bars, can

in many cases be difficult to handle during transportation. For example, a wall panel shall

be transported standing at the edge, but has reinforcing bars protruding at the bottom. This

will make it necessary to build up the support on the trucks, which is costly, takes time,

and makes the load less stable. This problem can be solved by letting the bars protrude

from the top of the element, but then the total height may make it difficult to negotiate the

underpasses en route. The solution may then be to have the protruding bars replaced by

insert and threaded bar, to screw in after the element has been transported to the site



If protruding units do not create the kind of problems described above because they do

not stick out that much, there still may be some difficulties. For example: corbels pointing

down during transport may necessitate a lot of additional support provisions for the

columns on the trucks. The consequence can be a less stable load, or decreased

loading capacity of the truck. This kind of problem can be solved by making columns

with the corbels in one plane only, and then place every second column ‘top-to-bottom’ on

the trucks. Otherwise it is also possible to look for a corbel-free solution.

ERECTION

It is the process of assembling the Prefabrication element in the find portion as per the

drawing. In the erection of prefab elements the following items of work are to be carried out.

1).Slinging of the prefab elements.

2).Tying up of erection slopes connecting to the erection hooks.

3).Cleaning the elements and the site of erection.

4).Cleaning the steel inserts before incorporation in the joints lifting and setting the elements to

correct position.

5).Adjustments to get the stipulated level line and plumb.

6).Welding of deats.

7).Changing of the erection tackles.

8).Putting up and removing the necessary scaffolding or supports.

9).Welding the insorts laying the reinforced in joints.

The erection work in various construction jobs by using prefab elements differs with risk

condition, hence skilled foremen, and workers to be employed on the job.

Equipments required for erection



Equipments required for the prefab elements in industry can be classified as.

1) Machinery required for quarrying of course and fine aggregates

2) Conveying equipment, such as but conveyor, chain conveyors etc.

3) Concrete mixers

4) Vibrators

5) Erection equipment such as cranes, derricks, chain pulley etc.

6) Transport machines

7) Work shop machinery for fabricating and repairing steel.

8) Bar straitening, bending and welding machines

9) Minor tools and takes, such as wheel barreriour, concrete buckets etc…

10) Steam generation a plant for accelerated curing

Planning co-ordination

It is important to have the precaster erector/installer and builder working together to achieve

best performance.

Site Access and storage

Check for site accessibility and precast panels delivery to site especially low bed

trailers

Check whether adequate space for temporary storage before installation and ground

conditions. (firm ground & levelled)

Uneven ground will cause overstress & crack panels.

Planning crane Arrangement

Plan the crane capacity and lifting gears based on

Heaviest weight of precast panels



Lifting heights.

Working radius

Position of crane in relation to final panel location

Plan other equipments

Boom lift and scissor lift for unhooking installed panels.

Lifting gears

Skilled personnel’s

Competent crane operators

Rigger

Signalled etc

General considerations for crane selection

Total lifting weight

Crane model

Crane safe working load (SWL)

(i.e) Based on 15% capacity build in F.O.S. 1.33

o Lifting capacity must be 1.5 times the total weight i.e) F.O.S 1.5

Lifting and swing radius

Crane counter weight

Crane boom length is relation to the vertical and horizontal clearance from the building.

Installation Process

Installation of vertical components

Verification of Delivered Panels

Check the panels delivered for correct marking lifting hook and position etc.

Surface finishing condition

Pc Dimension compliance

Reinforcement Provision/position



Architectural Detail compliance

1. Setting out

Check the panels delivered for marking, lifting hook and condition.

Set the reference lines & grids

Check starter bars for vertical components before hoisting for installation

2. Setting out Quality control point

Ensure correct offset line

Check shim pedal/plate level and firm

Rubber gasket property secured

For external wall/column place backer rod.

3. Hoisting, Rigging and Installation

While tilting provide rubber pad to avoid chip off.

Lift and rig the panel to designated location

Adjust the panel in position and secure

Lifting of space adding items with balanced centre of gravity.

Ensure horizontal alignment correct

Ensure panel vertically to correct plumb

Check panel to panel gap consistency

Check stability of prop before releasing hoisting cable.

4. Grouting works

Prepare and apply non shrink mortars to seal

For corrugated pipe sleeve on splive sleeve pour NSGT or proprietary grouts into pipe

slab.

Keep installed panels undisturbed for 24 hrs.

Check joint widths are consistent before grouting

Grout used should be same grade of components and self compacting to prevent

cracking.

Collect test cube sample for testing for critical element or load bearing elements

5. Connecting joints

Cast in situ joints install rebars as required

Set up forms for casting joints

Do Concreting



Remove forms after sufficient strength

For external connections sealant shall be used

Panel with welded connections welding as required

Installation of Horizontal Elements

1. Setting out

Set reference line/offset line to required alignment and level of slab/beam during

installation

Put temporary prop to support the precast slab/beam elements

Before Hoisting chem. Dimensions

Check level and stability of shim

Check protruding/ starter bars are within the Specified tolerance to prevent any

observation during the erection process

2. Hoisting & Installation

Put temporary props to support slab/beam

Lift and rig the elements in designated location

Align and check the level before placement

The beams shall prop atleast 2 location

Balcony planter box and shall be supported more than 2 location based on design

considerations

Check level of precast elements

3. Connections/Jointing

Precast with cast-in-situ joints place the lap rebars as required

Set formwork for casting joints

Remove formwork after concrete strength is achieved

Supporting beams shall be designed to form part of formwork joints

The connecting/lapping rebars tied & secured

Same grade of concrete 10 to be used that of panel.

4. Installation using Big canopy

Big canopy high rise precast concrete construction system

This is used for faster and efficient

5. Erection Purpose



In Japan

o Used to construct the 26 storey pre-cast concrete 30,763m2

o The system realized 60% reduction in labor requirement for the frame

erection.

In Singapore

o DBS China square used the system to erect is efficient and faster

6. Installation constraints Management

Example

The project requires precast panel to install 2 basements down.

Constraint

Temporary Decking for various for various works.

Cross bracing with king posts

No direct access for panels

7. Management

Roller frame and plat form was laid.

The panels lowered in roller platform

Push to underneath deck where panel is required

Remove of one deck panel to lift and install panel in correct position.

8. Mishandling of precast panels

Case Study

The hollow core slab was in the process of installation it was placed on the beam

corbel

For making adjustment in position the panel was lifted.

During lifting the panel was broken

Case of Failure

The panel was designed for simply supported condition

The lifting position with over 3 m cantilevered edge that has resulted panel damage.

Remediation

Use appropriate lifting position

Seek advice from precaster



9. Common Defects in precast panels

The common defects to hole in precast panels before installation panel before

installation.

Panel not property touch up.

Damage due to insufficient protection during delivery

Panel dimension deviation

Panel twisted no rectangular

Wrong rib and architectural detail

Missing starter bar or as wrong position

Corrugated pipe duck choked

Considerations for Erection

To fully realise this benefit of fast erection of a precast structure, and to keep the

costs within reasonable limits, field connections should be kept simple. In order to fulfil

the design requirements, it is sometimes necessary to compromise fabrication and

erection simplicity.

1. Use connections that are not weather sensitive

Materials such as grout, dry pack, cast-in-place concrete and epoxies need special

provisions to be placed in cold weather. Welding is slower when the ambient temperature

is low. If the connections are designed so that these processes must be completed before

erection can continue, costly delays may result.

2. Stability of the elements

Some elements may require propping, shoring, bracing or fastening before the

hoist can be unhooked. Planning for the fewest, quickest and safest possible operations to

be executed before releasing the hoist will greatly facilitate the erection.

3. Stability of the structure



In every stage of the erection process the stability of the structure as a whole must

be planned and assured. If not, costly additional measures may have to be taken. The

type of connection used may play a decisive role in this.

4. Be aware of possible different loading conditions during erection

During erection loading conditions can occur, which induce stresses or

deformations, as well in the precast concrete units as in the connections, which are higher

than those under service conditions. When designing the connections due consideration

has to be paid to these effects unless special measures are taken during the erection, such

as temporary supports etc., to prevent such situations.

5. Standardize connection types

All connections, which serve similar functions within the building, should be

standardized as much as possible. As workmen become familiar with the procedures

required to make the connection, productivity is enhanced, and there is less chance for

error.

Some types of connections require skilled craftsmen to accomplish, for example

welding and post tensioning. The fewer of these skilled trades required, the more

economical the connection will be.

6. Standardize sizes of components

Whenever possible, such things as field bolts, loose angles, etc., should be of

common size for all connections. This reduces the chance for error, and the time required

searching for the proper item.

7. Use connections that are not susceptible to damage in handling

Reinforcing bars, steel plates, dowels and bolts that project from the precast piece

will often be damaged in handling, requiring repair to make them fit, especially if they



o

I

are of small diameter or thickness.

Connection detail that makes erection impossible

Support solution that makes erection impossible



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